text:
Why are the F/A-18 rudders deflected in opposing directions during takeoff?
Looking at some videos and photos of F/A-18 Hornets and Super Hornets taking off from carriers and from airfields, I recognised that the left rudder is pointing right, and the right rudder pointing left.
Here's a picture:

Why is that? Are there any aerodynamic advantages?
Is it also used as an airbrake to slow the plane down at landings?
At which point of the flights are the rudders in this position and why? (Takeoff, landing, cruising, or both?)
Does the pilot steer them or is the work done by a computer?

Living Wing
The Super Hornet has a living wing, that is to say, the shape of the wing is constantly in motion throughout every regime of flight. Trailing edge flaps, leading edge flaps, stabs, rudders, and ailerons all move in concert to give the pilot the greatest control during particular phases of flight.
This is evident by the use of the flaps switch. The three flap positions are, Auto (Up), Half, and Full. Up auto means that the flight control system (FCS) will dynamically change the wing based on what it thinks the pilot is trying to do. However, when the flaps switch is placed in the half and full positions the FCS switches to landing mode, and all flight control inputs will be interpreted as such. Even though the flaps switch has been placed to half/full, the pilot has only changed the FCS logic, he has not actually commanded the flaps to a fixed position. There are no fixed gains (flaps positions) like there are in typical commercial aircraft. Instead, the computer adjusts the flaps position to mimic a flaps half/full position, while also giving the pilot the most stable platform it can for landing. The logic has its limits though and if the pilot exceeds 14 AoA in a landing mode (flaps half or full), the FCS may accidently depart the jet. This is obviously bad 200 ft above the ground.  This switch commands the FCS to make flight control decisions and is the toggle between the tactical, and landing modes of flight.
Rudder Toe-In
The particular effect you are referencing is called rudder toe-in. At slower speeds, particularly during high angles of attack, the stabilators may not provide sufficient nose authority to crisply rotate the nose. The massive wing area of the Rhino tends to block the airflow over the stabs. To remedy this problem the Rhino's rudders will automatically bias to the inside and create a downward force, which pitches the nose upwards. While the rudder is toed-in, the pilot can still use the rudders to yaw the aircraft. The FCS selectively moves the rudder position to generate the yawing motion, even while retaining the fared-in position.
Take-off and Landing
During takeoff the rudder will remain in the toe-in position for a fixed 10 seconds after it detects weight off the wheels. This prevents the aircraft from accidentally faring the rudders (and losing nose authority) during one of the most critical phases of flight (AoA probe failures will actually cause the rudders to automatically fare, and this problem is removed by a fixed timing.) During the landing portion of flight, the rudders will also be fared in to give the aircraft more nose authority, and this is handled automatically by the FCS once the pilot commands the aircraft into landing mode by placing the flaps switch out of up auto.
Other Functions
While the Rhino does have small speed brakes that extend during full speedbrake deployment, the primary method of increasing drag to rapidly slow the aircraft is through the use of the control surfaces. The FCS will increase the drag by lowering the flaps, toeing-in the rudders, lowing the ailerons, and deflecting the stabs, all while still giving the pilot a stable platform to fly the aircraft--it's an impressive aircraft.
During high alpha maneuvering, the Rhino will again deflect the rudders to the toed-in position while the flaps switch is in up auto. With the FCS logic in auto, the computers will attempt to retain control of the aircraft during max performance maneuvers, and will automatically schedule the flaps and rudders to compensate for high AoA and slow speed flight. Because the nose is cocked up and the airflow is disrupted over the stabs, the rudders will again create that pitching force that will assist the pilot in maintaining nose authority through any regime of flight.
Emergencies
As stated before, there are times when the rudders may suddenly fare themselves which can have devastating effects during the final portion to land. Rudder failures are serious problems and should be treated as such.  Higher landing speeds and extra caution will be used, and the pilot should understand that wave offs may be impossible due to lack of nose authority in close to the ramp.

Thanks for your answer! Are there any known incidents caused by rudder failures?

@jklingler  That sounds like a new and separate question.  You should probably post it as such.

@J... http://aviation.stackexchange.com/questions/19260/incidents-caused-by-rudder-failure

What does "faring" mean?

@cpast I believe I was ambiguous, I'll edit to use precise language when I have a minute

Perhaps you meant to use "fair"?

@Rhino driver, I was surprised to see you use the nickname "Rhino" to refer to the F-18. I thought this nickname was for the F-4 phantom, some research (http://www.coastcomp.com/av/fltline2/nickname.htm ) shows this. Where did you get this from?

@CharlesBretana From Wikipedia article on Super Hornet: "To aid safe flight operations and prevent confusion in radio calls, the Super Hornet is informally referred to as the "Rhino" to distinguish it from earlier Hornets. (The "Rhino" nickname was previously applied to the McDonnell Douglas F-4 Phantom II, which was retired from the fleet in 1987.) "

cpast , Rudder faring in this context means that the ruddes go back in initial position (don't stay toe-in) as should be at the moment of the final phase of landing .

Note that the rudder toe-in is already used in the original F-18A, not just the Super Hornets and their "living wings".

The rudders are deflected inwards during takeoff of the F/A-18E to help in raising the nose of the aircraft as it leaves the ship. As the vertical fins are canted outwards, deflecting both the rudders inwards generates a downforce, which, due to its location aft of the center of gravity, creates a pitch-up moment.
This position of rudders during takeoff is common to all F-18s, including the Canadian CF-18s, which are not used in carrier operations.

Source: mybirdie.ca
Almost all aircraft with a canted tail (F22, F35, etc.) can (and do) use their rudders for pitching in concert with elevators. The rudders are used during landing too. The principle is not much different and the FBW computer handles all these control surface operations usually.

Source: reddit.com
The rudders are also used as airbrakes. The F18 had an airbrake, which was removed in F/A-18E/F, and the control surfaces are used as airbrakes.

"FA-18 Trap" by Original uploader was E2a2j at en.wikipedia - Transferred from en.wikipedia; transferred to Commons by User:Mo7amedsalim using CommonsHelper.. Licensed under Public Domain via Commons.
The rudders are in this position during takeoff/landing and once the aircraft is cruising, they become inline with the vertical tail to reduce drag. However, they can be used for decelerating the aircraft in flight, if required. Again, it is the computer which does the work.

Source: www.f-16.net/forum/

The real reason: Ground effect was not considered during development.
Ground effect reduces the lift curve slope of lifting surfaces, and the low tail position of the F-18 makes this effect very noticeable during take-off. During development, this effect was not considered and, consequently, the F-18  could not rotate at the calculated speed when it went into flight testing. This increased the take-off distance and demanded an increase in pitch-up authority at low speed. As Jan Roskam explains in his book "Roskam's Airplane War Stories" (War story 108):

When the first F-18 fighter […] was flight tested at Patuxent River, it became evident that the airplane would not rotate at the predicted speed. This made the field performance of the airplane unacceptable. The problem was traced to an error in the calculation of aerodynamic forces in ground effect. This is particularly severe in case of a low placed horizontal stabilizer. As a result there was insufficient down-load capability to effect early rotation during the takeoff ground roll.
The problem was fixed by toe-in of the rudders. A squat-switch on the
main gear biasses the rudders to deflect inward while on the ground.
This creates enough positive pressure over the aft fuselage to effect
early rotation.
This fix, although impressive, came at a price. All
flight control software had to be revalidated. Also, the
squat-switches represented additional system complexity.

There is another reason: With rudders fixed, the F-18 is longitudinally unstable at angle of attacks between 7° and 11° (see left plot below). By scheduling the extent of toe-in over angle of attack (see middle plot), the airplane can be stabilized (see right plot below). The graph below is copied from this MIT presentation and should explain the trick nicely:

Note that the rudder toe-in is already used in the original F-18A, not just the Super Hornets and their "living wings".

Is the squat switch you refer to not already present in the system? It sounds like they could have tapped into the same Weight On Wheels signal used for other control systems in the aircraft. Does that use a different set of sensors?

@ChrisIversen: I guess you need to ask Jan Roskam. I would suspect that the toe-in is coupled with the flaps - there are enough pictures with F-18s already in the air and toe-in still active. Would make more sense, too. But Jan wants to make a point: Engineers should think of all effects in combination, and revalidation is really expensive.

@ChrisIversen: RhinoDriver has settled this for us already: "During takeoff the rudder will remain in the toe-in position for a fixed 10 seconds after it detects weight off the wheels." So there is a squat switch after all, and I agree, it should had been there before already.

@ymb1: That source is rather rudimentary. As I understand it, ground effect affects the zero-lift angle also and the impact on lift coefficient changes over AoA. At high angle of attack it reduces lift, that is what happened to the F-18 tail. Lift pointing downwards in that case, of course.

@ymb1: Right, the upward acceleration of air hits a wall because the full circulation pattern cannot unfold as it can in free stream. The AoA is a matter of geometric definitions, so the lift curve slope in the linked graph should not be straight. Please see NASA TN D-4228 – it shows a loss of lift near the ground at high angles of attack.

It's the rudders acting like a ruddervator to assist in pitching up. This is possible because they lean outwards a bit.


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What is the guy in green showing to the F/A-18E pilot before catapult launch?
In the following frames, you can see a guy in green showing a panel-like device with numbers on it to the pilot of the Super-Hornet that is about to launch from the carrier USS John C. Stennis.

What is this panel for?
What information is the pilot given?
Why just before takeoff and not while boarding/briefing?

(YouTube)
Edit:
I won't accept this question as a duplicate. It may contain the answer

Taxiing up to the catapult, a green shirt will hold up the weight board. If the weight on the board matches the weight on the weight chit, acknowledge ...

but the question isn't really about that part and quite "hidden".

Possible duplicate of What is the force exerted by the catapult on aircraft carriers?

@fooot I assume you are saying that he is showing the set catapult force to the pilot for verification purposes? I read the linked answer but it does not address what is displayed on that box.

In the accepted answer, a green shirt will hold up the weight board, which is what your pictures illustrate.

@fooot, ah, got it. The "possible duplicate" really isn't a dupe, but it is definitely related and happens to contain the answer.

If you're happy to consider Wikipedia as being accurate, and articles like this do tend to be since many people would correct and there is little motivation for others to mislead, then this article will help.

That's a weight check. The sign has the weight of the aircraft in pounds. The catapult crew guy first shows the presumed weight to the PIC who must give a thumbs up, agreeing, "Yes, that is the weight I believe my aircraft to have."
The crew guy must then show the same exact set of numbers to the catapult chief operator, who must also approve it: "Yes, the catapult is set to launch that weight.
You can actually see both verifications happening in the two photographs above, the first one is to the PIC, the second to the catapult operator. Only when both verifications have occurred will a launch be permitted.

I have no reason to doubt you, I'm just curious what your source is for that?

@FreeMan I am a civilian, but I do a lot of advanced research for the navy so I know exactly how CVN systems work, including their flight operations.

Sounds like fun!

Whats the units of that number?

@DavidGrinberg Pounds. At 44k that would suggest just a patrol flight or training flight with no ordnance. When an F-18 is loaded up with bombs it can be well over 50,000 lbs.

Is that number rounded? Seems hard to believe the aircraft would weigh 44k on the dot.

@DasBeasto yes - by the time you factor in safety margins and margin for error, there's no point worrying about being entirely precise. I believe they always round up, though.

@DasBeasto The CV NATOPS says Weight board will be changed in 500- or 1,000-pound increments in accordance with applicable aircraft launch bulletins CV NATOPS pages 4-4 and 4-5.  (There's an old copy on line in pdf form circa 1997).  This particular practice hasn't changed.

By the number spacing on the board, it looks like the final two zeros are closed up, so I'd guess they're permanently painted on and cannot be changed. The leading three figures presumably rotate or flip. Perhaps the 3rd figure only has 0 and 5 options.

I have to ask, why don't they have digital scales built into the deck for exactly this purpose? This appears to be a very crude, time consuming, and error prone approach.

source: Stack Exchange

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sort: votes


text:
What is a flameout and how does it occur?
I often hear the word "flameout". What is this and how does it occur?

Flameout basically means that the flame in the combustion chamber has been extinguished. A jet engine compresses air, then adds fuel and ignites it. So, it needs three things to function correctly- fuel, air (oxygen), and the heat to make them burn. Removing any of the three can cause a flameout.
It can happen for a number of reasons:

fuel starvation- Air Canada Flight 143 suffered flameout (due to wrong amount of fuel being put) and had to be landed like a glider.
Compressor stall (or surge)- The disruption of airflow due to compressor stall can cause an engine flameout.
Ingestion of foreign objects - British Airways Flight 9 suffered flameouts in all four engines due to ingestion of volcanic ash
Firing of armament- Early in its service A-10 Warthog suffered flameouts due to the engines ingesting the gassed generated while firing the GAU-8 Avenger.

Early jet engines (like the Jumo 004B) had high rates of flameout; however, modern jet engine flame outs are very rare, at the rate of about one every 100,000 non military flights. In most cases of flameout, the engines are restarted for resumption of flight.

Airspace magazine mentions a case where flameout happened because a F-100 ingested fuel (during aerial refueling); however, such occurrences are quite rare.

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text:
What is this smoke coming from an F/A-18 shortly before takeoff?
Watching a video of F/A-18 fighter-jets taking off, I noticed some sort of gas blowing out behind the canopy shortly before the start of the takeoff roll.
Here's a screenshot:

In some videos the smoke is more dense than in others. Has this something to do with cockpit pressurization?

I'm not sure which variant those are, but this cutaway drawing doesn't seem to have anything in that area that would be venting off.

@RonBeyer The planes in my picture are F/A-18C's and not super-hornets like in your picture. Maybe the super hornet uses a different system?

@RonBeyer The Swiss Air Force really needs to stop doing that chemtrail dispenser test as part of the take off checklist.  It's supposed to be an airborn check.  ;-)

Testing a tank vent during the checklist, perhaps...?

Slightly, OK... extremely OT, but are those green stripes on J5019 the proximity lighting that pilots use to find each other in close formation, radio/radar-silence, night flight?

@FreeMan Yes.

@fooot - thank you. I knew there was a question about it here somewhere...

Speculation, but: I recently saw a video of an F-22 starting up, and its APU let off a similar smoke, in around the same point on the fuselage (though below the wing). Could it be that the planes taxied up with only one engine on, and what you're seeing is the second one starting up? Seems rather late to be doing that, though.

Maybe the pilots had burritos before the flight

It is not smoke.  It is bleed air being blown behind the heat exchanger which forces cool air across the front of the heat exchanger, this is only happens on the ground. The left side of the aircraft has a secondary heat exchanger that is also cooled by a water spray nozzle.  The water is created by the ECS taking bleed air and cooling it.  The water is blown out by the bleed air so you can see it more on one side than the other. In the picture, it seems to be raining so the air being blown out is more visible because of the rainwater.
-6287 (Fixed-Wing Aircraft Safety Equipment Mechanic, F/A-18)

The two round grills on the left leading edge extension sit over the top of the RADAR liquid cooling system components like the reservoir and pump.
The gas you see escaping upwards is water vapour from the primary and secondary heat exchangers used in the environmental control system (ECS). These ECS components are part of the more specific air cycle air conditioning subsystem and sit just downstream of bleed air subsystem. Air is forced over the heat exchanger to make it more efficient for cooling. The vapour is more noticeable when it is wet or humid outside, and when the pilot throttles up.

Engine bleed air leaving the turbine compressor travels through a condenser/reheater then into a water extractor,  this water is sprayed from a jet ejector in front of the secondary heat exchanger in the LH diverter channel. What you are seeing is simply water vapour.


text:
If a stall is at the same angle of attack what is the stall speed?
So I of course know that the wing can stall at any angle of attack, but what then is the stall speed? Is that the speed at which the wing will always stall and it may stall at a higher speed?

Possible duplicate of What is the immediate cause of stall?  This should give you everything you need.  Also this one.

The stall will occur after a certain angle of attack is reached (related to the airflow). If the pilot had to maintain a level flight while slowing down the aircraft, they would need to increase the angle of attack. At some speed this angle will be the stall angle, slowing down furthermore without descending will stall the wing. The speed corresponding to the stall angle, in level flight, is (abusively) named the stall speed. Note the stall will not occur at this speed if the aircraft is not flying level (but the angle of attack for the stall will remain the same).


text:
Is the modelname of a flight management system chosen in accordance with the aircraft it will be used on?
I am looking for information about what modules (not necessarly partnumbers) are used in a flight management system of a relatively new airplane.
After having looked around for quite some time, I found this bit of information with a very nice scheme block.
The flight management system (FMS) they are talking about is the 737 FCMS. However it is not totally clear to me (even after having looked around online), whether this is the FCMS is the one being used for Boeings 737.
Is this the case? Or is that number just coincidence?

I can't answer specifically for this case, but generally the FMS is made by a third party and used across multiple aircraft types.

Yes, this is the system used on the Boeing 737. As the document mentions, it is similar to the system design on the Boeing 757 and 767 models.

It was pretty hard to find that information. Why is it so difficult to find some sort of technical info about FMS? This info isn't even from the producers themselves.

FMS systems are not really standardised, each manufacturer has their own way of doing things. The manuals and technical documentation are copyrighted and subject to non-disclosure agreements. Those who buy aircraft or maintain aircraft systems tend to be careful about information leaking out of their business. There are very few people who have an FMS on their desk to play around with, and those that do are also bound by strict NDAs.

How does it come that I found this info in that case if it is subject to NDA? So the FSM is not chosen in accordance with the aircraft on which it will be used, right?

Over time things become public. Airlines go bankrupt, old aircraft are scrapped, documentation gets around.

Even more than NDA's, it's about $. It costs money to buy an official manual from the manufacturers, and those are copyrighted so that they don't tend to end up in the public domain very quickly or very often. Not to say it never happens, but anything official from Smiths or Honeywell or Boeing probably won't survive on the internet very long.  Less official publications and study guides, maybe slightly more available.


text:
What causes the average speed difference between the JFK to DEN flights and the JFK to LAX flights?
I just realized shortest JFK - DEN flights are ~4h40m (280 min) and shortest JFK - LAX flights are ~6h (360 min). I'm talking about currently available commercial flights.
NY - DEN (straight line) distance is ~1625 mi, NY - LA distance is ~2450 mi (approximate measures using Google Maps' Measure Distance). So NY - DEN is about 0.663 of NY - LA distance-wise, while JFK- DEN flight takes about 0.777 of JFK - LAX flight time-wise.
In other words, going by distance, I would have expected JFK - DEN flight to be about 42 minutes shorter, or slightly under 4h. Any idea where the ~15% increase in flight time from what I expected comes from?

Different aircraft, different routes, spacing, arrival slots, it can be a number of factors, distance isn't the only thing that determines how long a flight takes.

Thanks @RonBeyer - yes, I understand that, I just found the difference quite big.  To put it another way - I expected that the differences would be happening on both routes, so given the variety you would have shorter ones on JFK - DEN. Or am I just imagining and this is common occurrence?

Also, commercial flights include estimated taxi time, so the flight time will scale differently than the taxi time which depends on the specific airports involved (i.e. taxi time at DEN will very likely be much less than taxi time at LAX).  Therefore, your ratio would make more sense (assuming the same cruising speed which isn't necessarily the case either) if it only looked at flight time instead of block (trip) time.

Thanks @Lnafziger - OK, I was not aware of that, thanks for clarifying. However, that only tips what I find unusual in the wrong direction, no? I.e. given this, the actual JFK - DEN / JFK - LAC time ratio (0.777 I calculated above) is even bigger if calculated using flight times instead of trip times.

Punching the NFDC preferred routes into SkyVector, I get ETE for JFK to DEN of 3:39 and and ETE for JFK to LAX of 5:14.  Based on your original numbers, that's an hour for combined taxi times on the DEN run and about 45 min combined on the LAX route.  The DEN route time seems to be padded by at 15 - 20 minutes.  Twenty minutes at each end is not atypical for taxi time allowance.

@Gerry That difference could be due to time of day as well (taxi time will vary depending on what time of day the flight takes place).

@Lnafziger  True.  It could also just be the airline looking at its historical flight data and recognizing some systemic delays for that route.  With the FAA scoring them for on-time performance, it doesn't pay to be over-optimistic.

There is certainly a difference, but most of it definitely has a good explanation. Most of it is overhead such as taxi time that applies to both flights (almost) equally. This has a relative big impact on short flights.
The taxi out time for both flights will be about 27 minutes; JFK is not exactly known for its quiet taxiways. Both flights will add about 30 nautical mile for their departure route.
Both flights will fly approximately great circle routes, probably less than 2% extra distance during cruise.
The LAX flight will typically do a straight in arrival, almost no extra distance there.
The DEN flight will typically do a full arrival, 30 NM extra distance there.
The taxi in at LAX is 13 minutes on average, and 9 minutes at DEN.
Let's assume that both aircraft fly 460 knot true airspeed with 20 knots headwind during cruise, so 440 knots ground speed.
My estimates for the total flight times are then:

JFK-LAX

GC distance 2150 n.m
Departure detour 30 n.m
Arrival detour 0 n.m (straight in)
Cruise detour 25 n.m
Total distance 2205 n.m
Taxi out: 27 minutes
Climb out: 60 n.m. @ 300 kts = 12 minutes
Cruise: 2085 n.m. @440 kts = 4 hour 44 minutes
Descent/Landing: 60 n.m @ 240 kts = 15 minutes
Taxi in: 12 minutes
Total time: 5h50 minutes
Margin: 10 minutes

JFK-DEN

GC distance 1400 n.m.
Departure detour 30 n.m.
Arrival detour 30 n.m.
Cruise detour 15 n.m.
Total distance 1475 n.m.
Taxi out: 27 minutes
Climb out: 60 n.m. @ 300 kts = 12 minutes
Cruise: 1355 n.m. @440 kts = 3 hour 05 minutes
Descent/Landing: 60 n.m @ 240 kts = 15 minutes
Taxi in: 9 minutes
Total time: 4h07 minutes
Margin: 33 minutes

Great analysis, thanks DeltaLima - so basically it's a combination of non-cruise overhead on short flights and bigger DEN margins? In hindsight this makes sense: 0nm flight would still be cited as a 40m-1h flight due to overhead + margin.

I did an analysis of flights in the last 6 weeks of flights to those destinations. Different airlines fly different aircraft to them. The only two aircraft I could find that flew to both was A320 and A321. Averaging out flight times and dividing it by the distances you listed I only found a 4% difference between the two. That could be accounted for by the extra time in cruise between the two. Here is a table with my numbers.

Note that the data included only one B739 flight.

Thanks TomMcW - that's a good catch, I should have considered the airplane types...


text:
Can ADS-B DF-17 messages with a non-zero remainder after CRC check be used?
For fun I've been using an AirSPy SDR (Software Defined Radio) to receive and decode ADS-B packets, primarily DF-11 and DF-17 messages.
The code is written in C++ and works reasonably well. It performs IQ processing / demodulation, packet extraction, CRC checking etc. As its output it generates AVR formatted message strings that are then served via a Listen Socket / Socket based interface. I then use Virtual Radar as a client to decode and display the data.
With regard to the DF-17 and DF-11 packets, I'm currently only forwarding the ones that have an Interrogator ID of zero, the so called "unsolicited squitters". i.e. Complete packets that have a zero remainder after CRCing.
I also receive / decode plenty of packets that have non-zero Interrogator IDs.
Can I use these for anything useful?
In other words, could I extract any useful information, positions, velocities etc. If so I could then re-write them as unsolicited DF-17 messages and pass them to Virtual Radar.
I am researching this to the best of my ability, but currently drowning in specs and documentation as there appears to be so much of it!
Apologies if I've miss used any of the jargon, I'm only a week into my project.

Welcome to Aviation.SE Max.

Messages with Downlink Format 17 are, as you know, ADS-B messages that do not require interrogation. As such the interrogator ID will be zero.
Frequently you will see that, after applying the CRC check, the CRC remainder is non-zero. This is caused by corruption of the ADS-B message between the transmitter (see note) and the receiver. This is partly because transmissions of multiple aircraft are unsynchronised so that they may overlap an become difficult to untangle. This overlapping is called garbling.
Since you have IQ information available, you may be able to de-garble overlapping message with some success. Also, you could try to do error correction using the CRC algorithm. Up to two rogue bits can usually be corrected, more than that becomes difficult.
To improve the performance of the CRC error correction you can again use information from the IQ sampling, by giving each bit a confidence value based on the shape of the received radio data.
If you are not able to correct the error bits (i.e. you have a non-zero remainder after correction), you should consider that ADS-B message as useless.

Note: there are a couple of aircraft flying with rogue transponders that transmit garbage DF-17 messages with non-zero remainder. They will be phased out in the next couple of years.

Ooops, hit return too soon! I found the documentation a bit confusing. It implied to me that the interrogator ID could be any valid number and that the packet was a response. It does make sense that it should always zero. I am already correcting 1 or 2 bit errors with good success on messages that CRC to zero. I also plan to try and spot suspect bits to improve the efficiency of the error correction, via the IQ data and illegal Manchester encoding states. This seems like a reasonable strategy and should not too difficult to implement....

According what I could find in Annex 10, DF-17 messages are always supposed to have zero interrogator IDs -- so if you get any of those that don't pass the parity check, they must have been garbled.
On the other hand, DF-11 messages will often be sent with a nonzero interrogator ID. As specified, the interrogator ID after removing the CRC will always be between 0x000001 and 0x00005F; you can use that to retain some amount of distinction between a garbled message and a legitimate all-call response.
Whether this is useful is a different matter, since DF-11 basically doesn't tell you anything except there's an aircraft with such-and-such 24-bit address somewhere within sight of your antenna. But if you also receive position squitters from the same aircraft, I suppose you could have fun building up a map of where in your coverage area interrogations from particular radar installations can be heard.

Thanks! Interestingly, about 50% of the DF-11 messages CRC to zero. Should I be rejecting these? I do build up a table of valid ICAO address to help filter the other received DF types. I'll start taking the 0x0x1 to 0x5F range into account as you suggest.

@MaxvanDaalen: Ah, I overlooked something. DF-11 squitter is used for TCAS, so you should indeed expect to get those with zero IID.

OK, thanks for the update!


text:
Does the F-16 have a speed limiter?
In an aircraft like F-16, how do the pilot prevent going faster than Vne (velocity, not exceed)?
From the block 50 manual it seems to indicate Vne is 800KIAS/2.05M.
I believe even the earliest F-16s could go mach 2, so the newer with their much more powerful engine should easy exceed 2.05 mach.
Is there an automated system that reduce throttle when exceeding?

The pilot controls the speed and makes sure it doesn't go too fast

I don't think the answer to this is very different from the answer to the same question about any other plane. I could probably pretty easily get the single-engine propeller trainer I'm flying at least well close to Vne by gaining some altitude then pointing the nose hard down and pushing the throttle to maximum. Not saying I'm going to try it, mind you. Likely much the same applies to a Boeing 777...

@MichaelKjörling The question is basically if there's hard limits in the FLCS system for airspeed, just like an Airbus does. (i.e. the FBW Airbus will put in an unoverridable pitch up command to prevent overspeed) I know the F-16 has hard AOA limiters (just like an Airbus), but not sure for airspeed.

Section V of the Block 50 F-16 Flight Manual, is the "operating limitations". It says:

MAXIMUM AIRSPEED OPERATING LIMITATIONS
Refer to figure 5 3. Maximum operating airspeed is 800 knots from sea level to 30,000 feet MSL. Above 30,000 feet MSL, the aircraft is limited to Mach 2.05.

The introduction to section V states (my emphasis):

The aircraft and system limitations that must be observed during normal operations are presented in this section..

What does "observe" mean? One might assume that means the pilot can just sit back and watch them automatically occur, or the pilot must "observe" them by knowing and acting apon them. As evidence it is most likely this second interpretation, the list of contents in this section appears to be many things that the pilot needs to do.

It does not seem like a list of things the aircraft does automatically.
But more signifficantly, the contents of the flight manual also includes a section describing the flight law control system (FLCS) limiters:

and:

There is no mention of maximum speed.
So, it looks strongly like the FLCS limits 4 things (AOA/G, roll, yaw, rudder authority), and warns you about some other things (low speed), but does NOT limit maximum speed.

Observed means the limitations should be respected and followed by the pilot.  Values give their should not be exceeded for safe operations.

@CarloFelicione. Yes, I agree, and maybe should have worded it more strongly in that direction. But the black and white evidence that really puts it beyond doubt is the contents of the section describing the FLCS limiters.

It even mentions in the same document:
"Maximum airspeed operating limitations may be easily exceeded in level
flight due to the improved performance engine excess thrust capabilities"

Be advised that, while it's very easy to find, the HAF F-16 manual you have cited is still classified.

Romeo, yes! "observed" means do it, just like "observe" the speed limit on the highway does.


text:
Are radar bars centered around the horizon or do they move with aircraft pitch?
Say I am in a military aircraft with a non-AESA radar.
The radar is set to scan 4 elevation bars, so when I fly level, 2 above and 2 below the horizon.
If I pitch 20 degs up, will it continue to scan around the horizon or will the bars move up with the aircraft pitch?

well is there a particular direction you are interested in?

Direction? If you mean sideways, then no.

If i understand your question, you are asking whether the vertical elevation direction of the radar antenna lobe is corrected for when the aircraft is in a pitched up position as compared to a level position. (Whether this correction would be done mechanically in older radars or electronically with AESA radars is secondary)
It probably depends on the particular aircraft and version.
But to my knowledge it is generally not. The antenna will keep its direction within the host aircraft and thus scan a higher altitude volume when the aircraft is pitched up.
Note that the pilot can change the vertical elevation range of the antenna by tilting it up or down manually at any time (if it is not locked on a target) and will probably do so in order to compensate for longer phases of pitch up flight.
As an example, this document is a description of the AN/APG-66 and -68 radar systems of the F-16 Fighting Falcon.
(It is a documentation for a general public simulator game, but you can be confident that it describes the function of the real aircraft very accurately)
See page 11, section "Elevation".
In the case of the F-16, the antenna tilt interface is part of the HOTAS controls, on the throttle:
http://falcon4.wikidot.com/avionics:hotas, see "Antenna Elevation Knob"
When a target is "tracked" or "locked" this is another matter. In that case, the antenna will generally move autonomously in order to keep the target within the center of its detection lobe as long as possible, both vertically and horizontally (azimuth), within what is physically possible taking into account the attitude of the host aircraft versus the target. (See the doc for this also)

You understood my question correct. However your answer seems to be the opposite of the answer from @mongo. So I am not sure which answer to accept..

Don't accept mine, i figured out i'm probably wrong. I will try finding other sources.

Without knowing what radar system you are dealing with, I will answer generally.
An AESA relies on an array of normally dipole antennas which are phase adjusted to enhance the gain in a certain direction. In a non-AESA environment, an antenna such as a forward looking radar antenna is normally a dish.  The dishes are mechanically articulated to change the focus gain of the antenna to a different spot.  Some articulate vertically only, but there are some which can articulate laterally.  Additionally, some can alter polarization.
If your radar is a WX radar unit, then normally just the pitch, or elevation is adjustable.  Some targeting radars allow lateral articulation which helps scan, identify and track targets both vertically and laterally.
To answer the OP question, if the aircraft is pitched up 20 degrees, and the radar is coupled to the aircraft pitch, then you can expect that the dish would pitch downward.  Although, in this example, 20 or 30 degrees is about the limit of most of the radar units I have worked with.
Finally, modern AESA antennas can create multiple beams, which permit active and concentrated energy on selected targets. A non-AESA dish antenna does not really have that capability, although several strategies and methods were used, particularly before the development of aircraft PESA and AESA antennas.  A PESA by definition has one lobal pattern, which can be articulated.  An AESA may have more than one.


text:
Is "Tally-Ho" used in ATC radio communication, specifically in the UK?
This question Are "Tally-ho" and "no joy" acceptable ATC terms for civil operations? concerns the use of the phrase "Tally Ho" to mean "target in sight" in civilian air-traffic-control communication.
It was largely answered (and somewhat asked) in relation to the US/FAA, where it is not acceptable but sometime heard. However "Tally Ho" is/was a British phrase, and my question asks the same specifically of British/NATS/CAA communication. Again, I'm interested as to whether it is actually heard, and whether or not it's generally considered acceptable.
I am aware that some efforts are made to keep English usage international, though most feeds/transcript I've heard from the US have an awful lot of regional idioms and phrasing in them, so I'm not sure the extent to which it is adhered to.
(For people outside the UK, "Tally Ho" is generally considered archaic and comically mannered in general life these days, even within the UK, which is why I'm particularly interested as to whether its usage survives here in aviation).

I'm not sure whether it's heard more in the UK, but it isn't part of the standard phraseology for ICAO member states, which basically means it shouldn't be used.

I don't recall it (and I think I would) from listening in on ATC at Heathrow and Gatwick in the 90s while working for NATS.

I have never heard "tally ho" used in civilian aviation and it not a recognised phrase so should not be used.  A civilian ATCO would not think positively about anyone using that phrase.
It used to be used in military comms in combat.  Its usage arose during WW1 when the Royal Flying Corps (and later the Royal Air Force) drew its crews mostly from the "officer classes" who, in general, were also fox hunters or supporters of the same.
"Tally ho" is the cry shouted out by a huntsman when the fox is spotted and the hunt is on.
I served in the RAF from 1976 to 1986. Then as a civilian in the military until 1993 and in that time never heard the phrase.  I suspect that it has died out since it is not standard phraseology and perpetuates stereotypes which have no place in modern, professional organisations.
A non-standard, but common phrase is a simple "visual", but the correct phrase in both civilian and military use is "traffic in sight".

I believe "Tally Ho" originates from WWII, not WWI. WWI planes did not use voice radios. However Tally Ho" was official code in WWII.

@DJClayworth Not so sure.  I'll try to dig out some definitive "first use".  My, albeit uncertain, belief is that one crew would shout to the other when a bandit was sighted.

No, Tally-Ho is not accepted phraseology in UK civil aviation, and in 14 years of flying in the UK I've never heard anyone use it. At non-ATC airfields you occasionally hear some non-standard phrases, often with a bit of humor, but I've never heard that one.
If a controller asks if you have visual contact with an aircraft you would just say "affirmative" or "negative", or you can say something like "G-BT is visual the traffic". If you are in the circuit (pattern) and you can see there's another airplane in front of you you can report "contact one ahead".
Tally-Ho is anachronistic, and you'd never use it conversationally except in irony.

No, "tally-ho" is not acceptable. CAP 413, the UK Radiotelephony Manual, defines a correct response to traffic information like this:

G-CD, traffic is a Cherokee upwind and a Tomahawk late downwind
Roger, G-CD
...
Traffic in sight, G-CD

The phrase "tally-ho" is not mentioned anywhere in CAP 413.

The short answer is no. It is never used by either controllers or pilots. "In sight" would be the term used by civilians.
It's true, that I have never conducted a survey. It was mentioned earlier that CAP 413 (which is the reference) doesn't mention it: that leaves us, I guess, with either the training we've received, if that was in the UK, or the little experience we have. I humbly have both. I completed my training years ago there and I fly, day in day out in UK airspace, from Heathrow to Bigin hill, London city, or even RAF Northolt, and have been doing so, for a good 17 years and counting. Again, in that timeframe I have never ever heard it.
On a side note, most if not all my British colleagues come from the RAF, and even with them I have never heard "tally-ho" or maybe as a joke amongst us.

It is, in fact, used by pilots. Whether it should be is another matter and the question that should be answered here.

@Davidricherby,True, i have never conducted a survey. It was mentioned earlier that CAP 413( which is the reference) doesn't mention it, it leaves us, I guess, with either the training we've received if that was in the UK or the little experience we have. I humbly have both. I completed my training years ago there and I fly, day in day out in UK airspace, from heathrow to bigin hill,London city or even raf northolt, and have been doing so, for a good 17 years... And counting. Again in that timeframe I have never ever heard it.Does that mean, no one has never used it ever...? Maybe, but that wo

@Heliomaster Now that that has been edited into your answer (always best to put it in the answer, rather than the comments), I think that's a big improvement. Downvote reversed -- thanks!

In Iran , in the fghter section of the air force ,  (fighter squadrons ) , we use Tally Ho for ( target insight ) and No Joy for ( target not in sight ) .
I flow F-4D/Es & F-14s in Iranian air force for 25 years & have 8 years war experience with Iraq ,  incuding 5 air kills with Tomcats .


text:
Boeing 737 engine shape

why the front shape of the engine of Boeing 737 aircraft is not round ?? can anyone explain ?


text:
Why does having a geometry-limited aircraft lead to lower VLOFs?
For this question, please have in mind these excerpts from the 14 CFR 25.107 - Takeoff speeds.

"(d) VMU is the calibrated airspeed at and above which the airplane can safely lift off the ground, and con- tinue the takeoff. VMU speeds must be selected by the applicant throughout the range of thrust-to-weight ratios to be certificated. These speeds may be established from free air data if these data are verified by ground takeoff tests."

and  VR must be:

"(iv) A speed that, if the airplane is rotated at its maximum practicable rate, will result in a VLOF of not less than —
(A) 110 percent of VMU in the all-engines-operating condition, and 105 percent of VMU determined at the thrust-to-weight ratio corresponding to the one-engine-inoperative condition; or
(B) If the VMU attitude is limited by the geometry of the airplane (i.e., tail contact with the runway), 108 percent of VMU in the all-engines-operating condition, and 104 percent of VMU determined at the thrust-to-weight ratio corresponding to the one-engine-inoperative condition."

My question is: why does having a geometry-limited aircraft lead to lower VLOFs? Is it because, since the aircraft cannot reach the angle of stall because of its limitation, the VMU for such airplanes is greater than the stall speed, and thus the maximum Lift Coefficient has not been reached and therefore it offers a higher safety margin regarding stall?

Unless someone can find an old 14CFR Part 25 ruling that has the explicit reasoning, I believe you are right to consider that the rationale for giving extra performance credit to airplanes that have demonstrated minimum unstick speed ($V_{MU}$) limited by tail contact is that they are not limited by aerodynamics. However, I should point out that the intent is to reduce the rotation speed ($V_R$) and not $V_{LOF}$, which is not a performance V-speed.
For Part 23 aircraft, which does not require $V_{MU}$ testing, 14CFR 23.51(c)(2) (pre Admt 23-64) requires $V_R$ to be no less than 1.10$V_{S1}$, or 110% of the stall speed for takeoff configuration obtained out of ground effect.
This mirrors the Part 25 requirement of 14CFR 25.107(e)(1)(iv)(A), which you have cited in the OP. The difference between the two is that Part 25 allows the applicant to lower the $V_R$ by taking credit for the ground effect and the rate of rotation, but also poses additional onus on the applicant to flight test the $V_{MU}$ (which is involved and high-risk).
Vmu can be limited by either:

Stall in ground effect, or
Stick pusher in the takeoff phase, or
AOA limiter (FBW only) in the takeoff phase, or
Tail contact with the ground (i.e. geometry limited).

In the last case, the aerodynamic capability of the airplane has not been reached. Therefore, 25.107(e)(1)(iv)(B) extends some credit to reduce the rotation speed. However, as specified in AC 25-7C, this credit can only be taken if the airplane is actually shown to be geometry limited from 96% to 100% of the lift-off speed ($V_{LOF}$) with the lowest thrust-to-weight ratio allowed for takeoff.


text:
With today's technology, why can't we find crashed planes
How can a plane just go missing? It's mad surely with the technology these days they could at least pin point the location of a plane. We have the technology to transmit pictures of Pluto back to Earth million miles but a plane goes missing and can't be found?! Even if my iPhone got lost, I'll be able to have an app locate it for me.

Pluto is easy.  You know where it is.  Your iPhone can only be found if it's switched on and connected.  What leads you to believe that there are any similarities between photographing Pluto, finding an iPhone and locating a crashed aircraft?  BTW, those Pluto photos took billions of dollars and use slower links than I had on dialup in the 1980s.

If the aircraft has the technology to be found, it will be found. Some have it, other not. That's only a matter of money. the plane can transmit its GPS position to any receiver, likely a satellite when it is over land or water without ATC control centers. Are you ready to pay for it, because it's coming?

Contrary to what you state, your smartphone cannot be found if lost out of reach of a wifi access point or a telco cell. that is your smartphone can be found on 1% of the Earth surface at most, and probably this is very overestimated. With the current technology aircraft are easier to localize; more than 1% is well covered by SSR and echo radar.

Having a technology and using it are two different things. As already noted, you are able to get pictures from Pluto because your tracking station knows where it is.
Similarly, the aircraft position is determined by Primary Radar, which literally scans the sky, but its effective range is limited and they are costly to operate. The secondary Radar locates the aircraft by interrogating its transponder, which provides the ATC with its location and speed. However, if the transponder is not working, there is no way for to detect the aircraft locations.
The aircraft can also communicate with the ground station using ACARS, but it depends on on board electrical system. The same goes for the ADS-B, which depends on onboard systems for determining its location and speed.
Its a bit like trying to find your mobile after switching it off. No app is going to work.
Assuming that the aircraft is involved in a crash, the Emergency Locator Transmitter (ELT) can be used to trace the aircraft. However, these are not mandatory in scheduled flights(though ULB is mandatory).
Satellites could help, but again, they should know where to look for.
The wifi or working mobile phones onboard could help, but these are yet to be implemented in any big way.
The next generation technologies under development will allow  real time tracking of the aircraft, but these are still under development.

While the other points are valid the other consideration is that between an observer on the correct side of the Earth and Pluto there is a couple of miles of air and then miles and miles of absolutely nothing which is no obstacle to light or radio waves.
Looking for a lost plane there is a better than 2/3 chance that it is under seawater which you cannot normally see more than a couple of feet through with visible light or RF, (this is why submarines are so hard to find and have to use ULF to receive notification to surface for messages).  Keep in mind that we have better maps of the moon than of the seabed.  From NOAA: "The ocean covers 71 percent of the Earth's surface and contains 97 percent of the planet's water, yet more than 95 percent of the underwater world remains unexplored."
Even if you are on a flat level stretch of ground the horizon is only about 3 miles away when standing on the ground so a parked airplane 5 miles away would be invisible on a flat featureless grassland.

Receiving data from Pluto if far more complex than receiving data from an aircraft just before it enters the water. Even when underwater, some buoy can be released to transmit radio signals. Have a look at the DSN infrastructure.

IF the plane has the equipment fitted and it is not disabled by the crash, etc. also that is the plane giving us it's location rather than us finding the plane - Pluto was "discovered" optically using 1920's technology 90 years later the vast majority of the subsea terrain has not been observed.

There is no difficulty at all to track a commercial aircraft, including over the water. But tracking thousands of aircraft at the same time requires an infrastructure and to decrease the cost also requires the collaboration of the aircraft equipment, which is not a problem technically speaking. What prevents to move on is the price to be paid by the passenger. But it will eventually be done in the coming years, under the pressure of the regulators, and because accidents frequency could increase due to changing weather.


text:
Where is the lateral position of the aerodynamic center?
There is plenty of literature that describes how to find the aerodynamic centers (AC) longitudinal position.
But where would it be lateral?
My guess is somewhere near 1/3 out the wing from the fuselage, but I do not know..or would it maybe be close to the mean aerodynamic chord line?

This is not an answer, but usually as we have two symmetrical wings, the center in on the symmetry axis. If the wings are loaded differently, then the problem is more complex.

Yes, and that probably why people are more concerned about the longitudinal position. But if an aircraft had only left wing, question is, where would it be..

That question is more relevant than the comments make it: It needs to be answered when the wing spar is sized. The sad truth is: There is a multitude of lateral aerodynamic centers, depending on angle of attack, flap settings, aeroelastic deformation and control surface deflection. It is calculated separately for each of dozens of load cases during design.

For a simple tapered half wing the aerodynamic centre spanwise location is at:
$$
y_{ac} = {{b}\over{6}} \cdot {c_r + 2c_t\over c_r+c_t}
$$
where $b$ is the span, $c_r$ is the root chord and $c_t$ is the tip chord.
For a symmetric aircraft it should be at the centreline, since it's the combination of the two identical (but opposite sign) locations.
Source is a aicraft sizing code I wrote some years ago, I remember solving the integral for a simple tapered wing.
Looking quickly at design books I can find the following image in Raymer, hope this helps:

Do you have any sources?

what do the various terms mean?

Added answers in my original answer!

Since an answer for an arbitrary wing shape probably would be pages of calculations. I am going to accept this answer. My question probably was too broad.


text:
How do I estimate how much air flows through the intake due to engine suction?
I read that the intake mass flow ratio (not sure its translated to correct lingo) can be expressed as:
$C_A = \frac{\textrm{airflow through air intake}}{\textrm{air density } \times \textrm{ speed of free flow }\times \textrm{ intake area}}$
A graph of this could look like:

Now my question is two fold:

What is the correct english term for this factor?
How do I estimate how much air flows through the intake due to engine suction.

Maybe the term is more like inflow-number. Don't know.
If for example flying at low speed and more air is sucked in that would normally hit the intake if it was only a tube, then the airintake factor is greater than 1. That how I understood it.

Okay, to solve this I assumed the atmospahere is ISA and flying at 0ft.
Also that air suction vary linear proportional to mil thrust.
So that airflowThroughAirIntake = factor*thrust
I then did some flight tests to estimate what that factor would be, getting the ratio from the graph at full mil thrust.


text:
Which FAA regulations require passengers to comply with flight crew instructions?
Recent unfortunate news headlines prompted a quick search for the almost universally un-cited regulations governing passenger compliance with flight crew, and all I could find were regulations that seem to be quite specific in application (14 CFR 125 - interference, etc.).
While it makes sense that passengers are expected to comply with reasonable requests, one would not expect the law to require compliance with unreasonable requests unrelated to safety, or requests that actually endanger passengers.
So, for example, if a crew member requests that a seated and non-disruptive passenger leave a plane for purely commercial reasons unrelated to anyone's safety, is there a law or regulation that supports this for US carriers?
Again, I expect the answer is "yes," but am interested in the legal basis for it, and do not think the self-serving fine print on an airline ticket qualifies.

note that when you buy a ticket you are also subscribing a contract with the company. it might not be an FAA regulation, but simply a rule in the contract that you as a passenger accept when you purchase the ticket.

@Federico: Contracts written by a merchant (in practice) may contain unlawful or unenforceable provisions. I would hate to be in court defending conduct on the basis of fine print. But even so, I would like to know precisely what the print says. As with regulations, contracts are subject to interpretation and (ultimately) common sense.

Btw, I don't understand why people are flagging this as off-topic, you are asking about FAA regulations. Even if they do not exists, this would not make the question off-topic.

@Federico: Thanks for the comments. I don't have the rep to see such flags. Interesting.

There is the common attitude here that anything relating to passengers should go on travel.SE, but personally I feel that this kind of regulation question is better dealt with here.

There's also the fine line between a law and a regulation. Normally, "law" enforcement officers don't have jurisdiction to enforce a regulation. The US CFRs are simply regulations that the executive branch writes in order to do their job of carrying out the laws passed by the legislative branch.  There is frequently overlap, where CFRs will specifically require something because it is also a specific requirement of the law. My point: you may find the "best" answer in Title 49 USC, as opposed to 14 CFR. (which, of course, might be better law.SE)

Here are some more research areas:  14 CFR 250 talks about overbooking and what is required in order to deny a passenger who has a ticket.  And it enforces laws in 49 USC 329 (spread out through 5 or 6 different chapters).

If there is a policy against including thanks in a post, please let me know and I'll edit. The word "uncited" is not idiomatic English, so I added a hyphen.

@daniel yes, generally thanks in a post are seen as redundant and distracting. the way we say thanks is by upvoting and accepting the answer that is most useful. also the title is preferred to be in question form.

On the day itself, the captain decides who gets to be on the aircraft when it departs. End of story, full stop.
Not abiding with this falls under the interference provisions you already mention -- or, more elementarily, it is trespass. Local law enforcement will help enforce the decisions if necessary.
Afterwards, if someone who didn't get to fly contends they had a valid and applicable contract from the airline that entitled them would fly, they get to duke it out in court for monetary damages.  How that turns out would depend on a lot of factors that are better discussed on Travel.SE or Law.SE.
The airline may lose in court, and if the captain's decisionmaking was sufficiently egregious (say, "there'll be no [racial slur]s aboard the plane I'm flying"), he may soon find himself out of job.  But the police who enforced the captain's decision on the day were still in the right to do so.  It's not their job to attempt to unravel contract disputes on the spot.

I will think about this answer. The first sentence may be true, but I asked about the legal basis in aviation regs and you don't really discuss it. The issue of non-private police enforcing contract/tort law is surely more complex than you have suggested in the second paragraph. The point of my question was not to question the authority of the captain but to ask about FAA regs underpinning that authority.

@daniel: Is there anywhere in the Anglo-American sphere where police will attempt to enforce contracts without being based on a court order.

Right. So, for example, malls often have to hire private security to eject invitees who are, say, wearing an offensive t-shirt. Are they trespassing? Their invitation is revoked, but the nexus with public safety is distant.

So the point here is that you don't want an answer, you want someone to agree with you.

@JuanJimenez: This answer is more or less what I would have given without doing any research. So I agree with it. But it contains no supporting details about the regulations. If all I wanted was agreement, I would have accepted this answer. In general, I do prefer that people agree with me, but I try not to attack them personally if they do not. Doesn't add anything to the conversation.

14 CFR Part 91.3 Responsibility and authority of the pilot in comand is the regulation you are looking for that gives the pilot the authority to decide, for whatever reason, who flies and who doesn't.

It would help to quote the regulation and explain how it applies to the question.

For example, this NYLJ note -  http://www.kreindler.com/Publications/NYLJ-Article-06162011.pdf - suggests there are commonsense limits to the authority under 14 CFR. If it is correct, or even in the ballpark, the answer above is not correct as stated. "[F]or whatever reason," as long as it's not arbitrary and capricious, would maybe be more accurate?

@daniel In practice the captain/PIC of an aircraft gets the same level of deference as the captain of a vessel at sea, so even if the reason is arbitrary and capricious ("I just don't feel comfortable with this person onboard, for no specific reason.") their decision generally stands & can be argued later (i.e. "You can sue the airline" - as described in the article you referenced).

I don't think commercial airlines operate under Part 91 but usually under Part 121.

I don't think it's so clearcut.  CFR 14 Part 91.3 states:

(a) The pilot in command of an aircraft is directly responsible for,
  and is the final authority as to, the operation of that aircraft.
(b) In an in-flight emergency requiring immediate action, the pilot in
  command may deviate from any rule of this part to the extent required
  to meet that emergency.
(c) Each pilot in command who deviates from a rule under paragraph (b)
  of this section shall, upon the request of the Administrator, send a
  written report of that deviation to the Administrator.

At what point is the pilot "in command." and is swapping out passengers part of the "operations" of the aircraft?  I'll give you that is is when it becomes a weight restriction issue, but in this case...
The International Civil Aviation Organization, definition the "Pilot in Charge" as: "The pilot responsible for the operation and safety of the aircraft during flight time."[1] Flight time for airplanes is defined by the U.S. FAA as "Pilot time that commences when an aircraft moves under its own power for the purpose of flight and ends when the aircraft comes to rest after landing."[2] This would normally include taxiing, which involves the ground operation to and from the runway, as long as the taxiing is carried out with the intention of flying the aircraft.
By this definition, the Pilot is not in charge, when the aircraft is boarding.

This cannot be correct. If a passenger assaults a fellow passenger, even if the plane is not yet under operation, who then has the authority to handle the situation? That is why the pilot boards before passengers. This may not be "flight time" but the pilot is still in command - that includes the power to exclude passengers unless the decision is arbitrary, and that decision will still only be reviewed after the fact.

The pax in the story that prompted this question was not removed by crew when he did not comply. He was removed by Chicago Airport police officers. I suspect that in the end the FAA will consider United to have acted within the context of 14 CFR 121.580 https://www.law.cornell.edu/cfr/text/14/121.580. They had a right to call the police and have the pax removed. And the pax has a long history of anger management and other problems. It will blow over.

@JuanJimenez: I am only asking about the FAA regulation. Whether the pilot's action would stand under the very weak standard of review is not part of my question. It would be surprising to me if that question ever gets litigated.

Actually this topic is very complex, and goes beyond FAA, DOT and other regulations.
A friend was departing Chicago, on a hot Friday afternoon, after a long hold, and heard from the cabin crew that a woman near the rear of the plane wanted to get off.  The aircraft had not taxied onto the runway yet, and by his recall, he was required to take the passenger back to the ramp.  The cabin crew tried to reason with her, but she was insistent, so he went back to the ramp. Of course this caused a chain of events affecting most passengers and the crews.
Later his actions were reviewed by the company, and it was determined that his action was the best possible one to take, given that the aircraft had not entered the runway.
The flight actually begins when the aircraft takes the runway, the company lawyers said. "Flight time" means something else, and is for purposes of logging.
I don't think one will find this scenario in the regs, and while 91.3 may apply, other customs, policies and prior cases dictated the most preferred outcome.
He doesn't work for United.

interesting--thanks.


text:
What construction standards are used to increase impact survivability of passengers in case of a crash landing?
There are several equations on the site about effectivity of passenger seats and restraints, and how beneficial they would be in case of a crash landing:

This question about lack of shoulder restraints
This question about possible decrease of fatalities when using a shoulder harness.
This one about the best brace position.
This one on turning the seats backwards.

The latter one is the only one of the four that cites any research and quantifications on increasing survivability rates in a crash.
What are the requirements imposed on airliner seats and restraints in order to make sure that preventable deaths from impact are actually prevented? What research has been conducted to improve safety standards in the last few decades?

Performance Standard for Seats in Civil Rotorcraft, Transport Aircraft, and General Aviation Aircraft, SAE AS8049, for oblique seatings: SAE AS6316, implemented as (E)TSO-C127, FAA test procedure in AC 25.562-1B

The far out best overview of research is the Aircraft Crash Survival Design Guide (link to the first of five volumes, PDF). Sorry, there is no equivalent for civilian passengers.

The trick is to not crash in the first place.  Spend the money (and weight) and effort where it's needed. ;)

History
Research on occupant survivability of impact is over half a century old, and serious advances in knowledge about the subject were made through Colonel John Stapp in the 1950's. He successfully survived a 46.2g deceleration, as documented in this clip.

Colonel Stapp also tested accelerations up/downwards. backwards and sideways. From this fascinating article:

Stapp’s first project was analyzing plane crashes, or rather, why people were crashing in planes. Going into the project, the years prior and throughout the Second World War aircraft engineers and designers decided that humans could survive at a maximum of 18G 3. Airplane cockpits then were all designed to withstand 18G impacts because if the person was already dead, why invest in stronger materials and structural support. Just how this figure was achieved, why, from whom, etc. immediately came into question by Stapp and his group who had been carefully reviewing vast amounts of accident reports that had started to reveal some contradictory evidence against this number.

The article is from the Motorsport Safety Foundation, and indeed according to the Wikipedia article, Colonel Stapp was

..chairman of the annual Stapp Car Crash Conference. This event meets to study car crashes and determine ways to make cars safer. In addition, Stapp was honorary chairman of the Stapp Foundation, which is underwritten by General Motors and provides scholarships for automotive engineering students.

Advances in car crash survivability thus were started in military aviation, then further advanced and applied in the motor car industry. Civil aviation has been a laggard, partly explained by the very few accidents and the high proportion of fire on board after crashes: passengers who survived the crash then succombed in the fire.
Crash survivability is discussed in this 1980 Flight Magazine article as well, including the following table showing that cicil aviation specs were lagging behind military and flight medical recommendations:

Civil Regulation standards
Passenger aircraft manufactured before 2009 had to comply to the following safety standards for seats and safety belts:

14 CFR 25.561. Accelerations that the seats must withstand, demonstrated with tests using dummies:

Upward, 3.0g
Forward, 9.0g
Sideward, 3.0g on the airframe, and 4.0g on the seats and their attachments.
Downward, 6.0g
Rearward, 1.5g

14 CFR 25.562. Requirements on testing with a 170 lbs test dummy and:

nose down 30º, peak floor deceleration > 14g
nose level, peak forward deceleration > 16g, yawed 10º to demonstrate the capability of seat restraint to successfully restrain the passenger when side forces apply.
maximum levels of impact force for pelvis, head, legs.
requirement that the seats must remain attached at the end of the tests.

14 CFR 121. Under A. History, the text describes what improvements to standards were made to seat and seat restraints structural requirements.

Amendment 25-64 upgraded the certification standards for occupant protection during emergency landing conditions in transport category airplanes from only a 9g static standard to an upgraded 9g static standard and a new 16g dynamic standard.

Not civil, but the best: Aircraft Crash Survival Design Guide, link to pdf of first of five volumes, pointed out by @Peter Kämpf
Research projects

The Cherry study, discussed here, made recommendations for implication of measures and for further study.
The European Transport Safety Council study, further building on the Cherry report and making additional recommendation. The study states its limitations very clearly, yet distills methods for further improving survivability.
Studies into use of airbags, such as mentioned here.

In the US, the FAA has no requirement for crash integrity or safety of the air-frame (and they have been heavily criticized for this). There is no requirement for crash analysis like is done for automobiles. The only requirement is the seat integrity. From 1988 to 2009 the FAA has phased in the requirement for the seat and restraint system to remain secure - from 9G to 16G. New York Times
This is similar to the question,
"Why are passengers not given the option of shoulder harnesses?"

[Safety Report]


text:
What is the Scaling Factor in ARINC 429?
I'm a newly appointed engineer in an avionics company and have been tasked with preparing a report on ARINC429. I understand most of it, and I certainly find it simpler that 664, but I still can't manage to wrap my head around what "Scaling Factor" is.
No resource on ARINC429 I have found goes into detail about this, and the best I could find is image below.
This is a screenshot from a link discussing the standard.
Could anyone please explain what this is trying to convey?

Thank you guys!! The three answers took three different approaches to answer my question, and in the end I got a three dimensional understanding of the answer!! Cheers!

In the example you pasted, the value $1.5_{10}$ is being sent, which has binary representation $1.1_{2}$. The data is sent as an unsigned integer so some kind of multiplier needs to be applied. The value occupies 19 bits, at offset 11 within the packet itself being bit 0 of the data. The default multiplier is such that the "units" bit (ie the one representing $1_{10}$) is in bit 26 in the packet, that is the bit 16 of the value. You can see that in the first example, the lefthand $1_{2}$ is in bit position 16 (counting from 0 from right).
This allows only values up to slightly short of 8. Various scalings are applied to values, depending on the label, as this may not be a convenient range for the data conveyed. If a label conveys data in the range 0-6, then it is fine as is. If 0-65 must be conveyed by a label, then the value is shifted right four places (to give more space for the larger numbers, but with less precision). Which scaling is applied is determined by the label. If a negative number is possible in a type, two's complement is applied. The label definition determines the range of its various words.
You can see this example effectively repeated immediately with value $1.25_{10}$, which is $1.01_{2}$.

Great answer! I have one last doubt, the ranges mentioned are the scaling factor themselves or are they simply the data being scaled/encoded?

The example given is a bit strange in that it explains how to code a specific value as the scaling factor changes. In using A429, we don't often think in terms of how the scaling factor modifies the coding of a specific value as the range (scale) is fixed for any specific A429 label. To code a value, we look at the what the data type is and the range/resolution of the associated A429 label.
A429 binary number (BNR) labels are coded using two's-complement. With that, each bit starting at the MSB represents half the value of the previous bit. The scaling of a specific label is defined in Attachment 2B of ARINC 429 Part 1.
The 'Scaling Factor' you question is determined by the desired range of values with the resolution driven by the range and the number of significant bits. To scale the data in two's complement binary, the MSB is set to represent half of the +/- range value. Each successive less significant bit represents half the value of the previous bit. The resolution is the value represented by the LSB.
So, for example, Label 162 from an ARINC 712 ADF receiver (Equipment ID 012 hex) contains ADF Bearing data.  There are 12 significant bits and the range is defined as +/- 180 degrees. Bit 29 is the sign bit. Bit 28 (MSB) is 90, bit 27 is 45, bit 26 is 22.5, etc. down to bit 17 which represents 0.044 (sometimes rounded to 0.05 - I don't know why). So all 0 is 0 degrees (North). All 1 except for sign bit would be 179.95 degrees. A sign bit of 1 and all 0 (-0) equates to -180 in two's complement.
For other parameters you need to evaluate the data within Attachment 2B to determine the proper coding based on the range, number of significant bits, etc.

@mins  See edited text.

Yeah, I've found the "Resolution" field to be a little confusing because some are exact and some are approximations. The table in Attachment 9A (GA Labels and Data Standards) has the column listed as "Approx. Resolution". The exact resolution should go in that field just fine.

Another useful answer I can only upvote. This was significantly more than just "useful". Thanks mate!!!

The mistake I think the link is making is that number of significant bits determines the position of the LSB. The scale factor can influence the necessary number of sig bits, but the desired resolution does as well.
The easiest way I've found to calculate the value that actually gets inserted into the label is as follows:
The scale factor (which I'll call $Range$) is usually the value given, unless a $\pm $ is used, i.e. $\pm180$ for labels like heading, in which case you would use the highest value (180). The label you are sending should provide you with the correct number of significant bits. ($SigBits$)
The exact resolution can be found by $$ \frac{Range}{2^{SigBits}} $$
and the normalized value is
$$ Normal = Value *\frac{Range}{2^{SigBits}}  $$
Now you can take that value in binary, place the LSB so that there are the correct number of significant digits by padding 0's on the left. Anything right of the LSB is padded with 0's, to a total of 18 bits (19 for a signed value) - the width of the data field.

I just realised that I can only select one answer. I just wanted to thank you for answering the question

@selectstriker2 You make good point. The logic behind defining A429 labels can vary substantially between solid design and somewhat arbitrary. In my example of ADF bearing there's 12 bits out of 19 available. But with the accuracy of the ADF and the display resolution of 1 degree, 9 or 10 bits would likely more than adequate.  OTOH, LAT/LON labels presented a challenge to meet the needs of RNP. The MSB is fixed by the range. To get the needed resolution, we need more bits than available in one label, so we have two labels where the data bits are concatenated.


text:
Was there a historical requirement to announce altitude, temperature, etc?
It is a common experience of flying on commercial flights that pilots announce certain flying conditions, including altitude and speed.
It has been previously asked on Aviation SE why pilots announce the cruising altitude of flights.  The answer there suggested there was "no real reason".
On Quora, it was asked similarly why pilots frequently announce altitude, outside temperature, and speed.  The first answer there suggested it was previously a historical requirement; however, the answer does not provide a reference to these requirements.
Has there been historically, or is there now, a requirement in any major jurisdiction (FAA, EASA, etc.) for the pilot (or flight crew) of a commercial flight to announce altitude, outside temperature, speed, wind, or weather conditions?  If so, what was/is the specific text of the requirement?

I know of no requirement to make such announcements, but I often did for the simple reason that I thought some pax might be interested.

I would guess that if there was a historical requirement it would be a company requirement (e.g. Pan Am, etc.), not a regulatory requirement.

Possible duplicate of Why do pilots announce the cruising altitude of a flight?

@Notts90: That is the first link in my question, and my question is not the same.

As this may be most common among airlines, this is not a requirement whatsoever administered by the FAA or any other aviation governing body. This is more so considered a tradition usually when the plane reaches cruise or is about to land. No such modern airline or any airline in the past has required this to be announced to its passengers.

"No such airline" is a pretty broad statement. Is that all currently flying airlines? Is it all airlines that have ever flown? Do you have anything to back that up? I'm not saying you're wrong, some supporting evidence would make your interesting answer (which is in line with the comments on the OP) much stronger.

I did some research @FreeMan and no result seems to state required announcements that the crew has to give to the passengers relating to what the question other than safety concerns such as in emergencies. I also fixed my answer a bit.


text:
What are the five leading theories for lift generation?
I don't know if you guys have seen the British comedy quiz show QI (brilliant show), but in episode 10 of series A (aptly called Aviation) Stephen Fry (the host) mentions that there are five leading theories of how lift is generated, but none are validated. he then goes on to say that this only affects out understanding of lift and not how we engineer wings.
Now I am aware of maybe two prevalent theories (Bernoulli's principle and Coanda Effect), what are the other three he is referring to? And would an approximate theory (or an empirically sound hypothesis) be enough to design aircrafts?
Edit: I am aware of the fact that our understanding of lift is pretty watertight. I just wanted know if there were other hypotheses that used to compete with our current theory. (They could have been proven wrong, I just wanted to know them)

QI is a great show but you can't believe everything on it.

At times it does feel like they give shock-value more weight than fact-checking. Otherwise the General Ignorance segment would be finished by now. I just thought maybe I missed something my Aerodynamics classes.

At the end of the day it's entertainment, occasionally there's something said on the show that's fundamentally wrong but they get it right most of the time.

So can go back to thinking that there are only the two theories?

I didn't say that....

xD hahaha. Cheers, I'll keep my ears open for any answers.

Added an edit to explain why I think my question is different. Hope this clarifies things

@MichaelThomas I've seen it, but personally I think that the other question contains a good brief summary of various descriptions of lift that basically are your "five theories of lift generation"

I can't find the button to accept Federico's comment as the answer. According to this question it might have gone after I edited my question. If a moderator could close this question for me that would be great!

We leave duplicate questions up as guideposts to the duped answer. No need to delete. I don't know if the other answer says this, but more than one "theory" of lift can be true. For example, the Bernoulli concept of speed vs pressure is working at the same time as Newton's equal and opposite reaction. They're not mutually exclusive. NASA has a good series of pages on which theories are debunked.


text:
How is engine management being done without auto throttle during a VNAV approach?
I am wondering how the engine power is controlled if Auto-pilot in a coupled approach mode with VNAV capability, and the aircraft is not equipped with Auto-Throttle?
Is the pilot continuously adjusting thrust levers (or power levers in the case of turbo prop) to maintain appropriate angle of attack, as the speed, decent rate and heading is controlled by the auto-pilot...?!!
Or...there is no such thing as auto-pilot with VNAV capability and no Auto-Throttle.

The auto-pilot in a lot of small aircraft don't have auto-throttles and can fly coupled approaches. It is up to the pilot to control power. I think you misunderstand something though, a VNAV approach in a non-autothrottle aircraft can't control the speed (only descent rate). The autopilot changes the pitch to get a specific descent rate.

There are three jobs an auto pilot/auto thrust (or auto throttle) must perform:

Determine the aircraft pitch (and auto trim as needed)
Determine the aircraft bank (to seek desired heading/course)
Determine the aircraft thrust

Without an auto throttle/auto thrust, we remove item #3.
Another way to look at it, which is quite un intuitive is to understand the various possibilities of pitch vs throttle usage.
During climb, typically we want thrust set at a fixed maximum safe level and pitch is changed to sustain an optimal (or ATC mandated) IAS/Mach speed.
For that purpose, FADEC is enough to keep the throttle at that max safe level.
During optimal descents, we want the thrust levels at flight idle, and pitch is again used to maintain an optimal IAS/Mach speed.
During cruise we can either be thrust limited or airspeed limited. If there's enough excess thrust to keep airspeed, the thrust levels will be finely controlled to achieve a certain airspeed, or if there's a small thrust shortfall, max safe thrust levels are kept, and airspeed fluctuates with turbulence/changes in temperature and other factors that either change real thrust output or little pitch changes are needed to maintain altitude.
During approach what we often have is seeking a certain speed and a certain descent ramp (resulting in a required vertical speed), which requires thrust to the nearly always changing to achieve all of those two targets simultaneously. So an aircraft without auto throttle will require constant little thrust changes, but the actual vertical profile can be kept by the auto pilot, just respond to airspeed changes.
With modern EFIS, there's the airspeed tape that has a 10 second trend tape. This tells you where the airspeed is predicted to be 10 seconds from now if nothing else changes. So as long as airspeed is close enough to target speeds, just add thrust if the trend line is negative (until it zeros) and reduce thrust if the trend line is positive (until it zeros). If airspeed is a few knots off, add just enough thrust that the trend line gets back to your target airspeed just about 10 seconds from now (or perhaps have the trend line be twice as much as the deviation so you get be back to normal 5 seconds from now). That's actually quite easy to do with the trend line.
Autothrottle is quite important if you need to keep a precise thrust level to finely optimize fuel consumption. On smaller private jets that's usually not critical.
So the auto pilot does fly the VNAV approach or VNAV profile, without an auto thrust/auto throttle, your job is to control the airspeed, which is usually far easier with the trend line.
A related useful information is that on the top of the PFD (primary flight display, the one with the horizontal attitude, airspeed+altitude tapes) if you look on the top, in aircraft with auto throttle/thrust you will see 3 columns:
The left one shows what the auto thrust is doing (idle/thrust reference/air speed/...)
The center one shows the lateral navigation (heading/course/lnav/localizer/rollout/...)
The right one shows pitch control (altitude holding, vertical speed, speed, vnav, glideslope, flare, ...)
On aircraft with EFIS but no auto throttle, I think the left column is still there, just to tell the pilot what to do with the throttles, like a nice teacher.

Thank you for that thorough response. Excellent explanation. I get it now.

Hercules-63, if the answer is that good, how about an upvote ?

Done. I am new to the site, was not sure if this was an option. Know it now. Thank you again Marcelo Pacheco.

That's just fine. I edited the answer, adding some more comments about where you will find the information of what the autopilot and throttle is doing (or what they pilot should do if the autothrottle is disengaged or doesn't exist, in the same way that when the autopilot is off, the flight director probably is still on, and the pilot can follow the flight director and validate its doing the expected job checking up top the thrust/course/pitch references.

Is the pilot continuously adjusting thrust levers (or power levers in the case of turbo prop) to maintain appropriate angle of attack, as the speed, decent rate and heading is controlled by the auto-pilot...?!!

In 747-100/200 operations at the two 747 carriers I flew for, if you chose to have the autopilot fly a coupled ILS approach and didn't have auto-throttle capability, the autopilot tracked the glideslope by changing the pitch of the aircraft.
Personally, I never did this because I preferred to hand fly all approaches, but I watched others do it when I was the non-flying pilot, and they did indeed continually adjust the thrust levers as necessary to get the desired speed, just as we did when hand flying the approach.
In the 747 classics this wasn't hard. Initially you set the thrust levers to a fuel flow of 5,000 lbs/hr per engine, maybe a little less if very light, maybe a little more if heavy. Often that initial setting would give you the speed you wanted within a few knots and no further adjustment of the thrust levers would be necessary until starting into the flare. If it didn't, you adjusted as necessary, and with experience it took very little jockeying of the thrust levers.

Thank you for the response and great information. I appreciate it.


text:
How to calculate the DC-4 landing distance with this graph?
Can someone give me a clear explanation on how to calculate the landing distance of the Douglas DC-4 with the following graph? And why is the Temperature variable not in the graph, because temperature also has an influence on the LDR?
Thanks in advance.

Follow the arrows in the graph.
You start with the gross weight on the right X-axis and move straight upward until you intersect the correct field elevation. In the graph the line starts at 58,000 lbs and moves up to a field elevation of approx. 1700 ft.
From there move left into the left side of the graph. There, the X-axis is the effective headwind speed. Note the remark above the graph: This is 50% of the reported speed when the data for this graph was collected. Now you need to find the intersection of the line from the right half with the line vertically up from the headwind. Where both cross you take an interpolation of the landing distance lines. In the example the headwind is 18 knots, so the landing distance becomes 2000 ft.
Yes, temperature would have an effect, but for the landing distance that effect is small. A colder air is denser and reduces all speeds, so a shorter landing distance will be possible in colder air. But compared to a take-off where air density has a much stronger influence on engine performance, this effect can be neglected for a landing chart.


text:
Is it possible to get a purely VFR job with colour blindness?
I'm 23 years old and I have red-green colour vision deficiency. I'm currently working in engineering but I have my PPL and I've been interested in commercial flying for a very long time. I've always assumed I'll be unable to get the medical needed to follow a flying career anywhere.
I wonder if there are any opportunities for flying purely in VFR, i.e. Bush flying and that sort of thing, where all flying takes place during daylight hours? Are there any airlines or other flying companies that I'd have a chance with?
Thanks, any input is really helpful :)
PS: my location is the United Kingdom.

Welcome to Aviation.SE! Please add your location to the question using the edit button as the answer will likely depend on it.

I don't know how color deficiency is handled in the UK, but if you were in the US, I would advise you not to assume that you cannot fly commercially with your color deficiency. I would instead tell you to try for the highest class medical you can get with your deficiency. Here in the US I could not pass the usual color test for a 1st class medical, so they granted me a waiver based on passing a practical test, i.e. seeing correctly lights flashed at me from the tower. The waiver was permanent; I only had to do the practical test once over the course of many medical renewals

Thanks for the reply :) that's very interesting. When I did my class 2 medical, they recommended I take a 'CAD test' which is supposedly one of the more recent non-Ishihara tests. I think I'll take it as soon as I can just to see what they say. Even if I fail, perhaps I can get a professional opinion on what options I have left.

The CAD test is a computerised test that is tailored to aviation. Some people who fail the Ishihara can still pass the CAD test so you should definitely give it a shot.

I don't know enough about UK aviation to post an answer but it's not known for it's GA industry. You might be able to get an instruction job outside of those mass-production schools (the ones tied to airlines). If you're willing to move internationally you might have a better shot, like the Brits in this show: https://uktvplay.uktv.co.uk/shows/bush-pilots/watch-online/

There is another test, called the Farnsworth Lantern test, which you can take.  Not many aviation medical examiners have the lantern, so you might have to ask around, but if they have it and you can pass with that, you meet the medical criteria.
The waiver that Terry discusses is the SODA (or statement of demonstrated ability).  I had to get one for nearsightedness when I got my Class I, which consisted of a trip to the local flight standards office, a checkride with the FAA inspector who agreed I could fly just fine with my fully corrected 20/15 but uncorrected >20/200 vision.  There are plenty of airline pilots floating around with waivers of this type.

The FALANT is not a reliable test - the likely reason so few AMEs are equipped to administer it is that it frequently misses even dangerously-severe degrees of colorblindness.


text:
Why is it advised to turn the aileron away from quartering tail-wind during taxiing?
This question is related to a single engined cessna tricycle gear airplane. e.g, C152/C172.
The theory states that if the quartering tail-wind is from the right, the aileron needs to be all the way to the left with elevator held down. Can someone explain the physics behind this?
I understand this when you have a quartering headwind from the right. In this case you set the aileron on the right thereby reducing the lift on the right wing and increasing the lift on the left wing. This helps keep the right wing pressed down. But somehow the picture is not clear for the quartering tailwind.
Another way to look at this is to look at the wind as a vector. For a quartering headwind, the wind can be thought of as a wind component from the front and a wind component from the right. The wind component from the front is not a problem and the wind component from the right is balanced by the ailerons as discussed earlier.
Taking a similar approach for the taiwind from the right, the wind component from behind is taken care of by the elevator. That leaves only the wind component from the right. So the same aileron action should be required. But the books state the complete opposite.

The mnemonic that I use is, "climb into headwind, dive away from tailwind."
To address your question.
When the wind is a quartering tailwind, the tailwind component tends to want to lift the tail of the airplane, which could cause a prop strike or the airplane to be flipped over if the wind is strong enough. So by having the elevator all the way down, the wind hitting the tail will push the tail down instead of lifting it up.
The quartering tailwind hitting the trailing edge of the up-wind wing can lift the wing, so by diving away from the tailwind, the upwind aileron will be in the down position, which will help hold that wing down.
With regard to the physics of how this works, it has to do with the direction in which the wind is being deflected. When wind is coming from the front (headwind) an up aileron deflects the air up and pushes the wing down, but when the wind is coming from behind the wing, such as in a quartering tailwind while taxiing, the wind would catch an up aileron and lift the wing, so it is necessary to put the aileron down, so that the wind is deflected upwards thereby pushing that wing tip down.

This is the part I don't understand: "The crosswind component hitting the trailing edge of the up-wind wing can lift the wing". For a right quartering tailwind, I believe the up-wind wing is the right wing. If you want to reduce the lift on this one then the aileron control/yoke should be on the right?

I see where you are confused. Maybe if you think about the deflected wind, that will help you visualize what is happening. The down aileron on the up-wind wing is deflecting quartering tailwind air upwards, as the air hits the surface of the down aileron. As you know air that is deflected upwards will result in a  downward force on that wing, helping to hold it down so that it isn't lifted up causing the aircraft to be flipped over.

Yes, I think you are right. This is what I found in another book just a few seconds ago. The down aileron prevents the wing from flowing under it and lifting it.